Analysis and Optimization of Voltage Balancing Control Limits for Cascaded H-Bridge Rectifiers

Many methods have been studied to balance the capacitor voltage of the cascaded H-bridge rectifier (CHBR). However, these balancing control methods will fail while the difference of the dc-load connected in each cell exceeds the operating limitation. Therefore, it is necessary to analyze and optimize the limitation of the balancing control quantitatively to avoid the failure of the control system. In this article, the voltage balancing limitation (VBL) is quantitatively derived and the stable operation region (SOR) is analyzed. Moreover, essential factors affecting the balancing ability are screened out. Then, the VBL and balancing dynamics of two typical methods are elaborated. And three novel methods (Methods 1-3) are proposed to improve the balancing dynamics and extend the VBL. The effects of the five methods are compared. Finally, the correctness and effectiveness of the theoretical calculation and optimization methods of VBL are verified by the simulation and experimental tests. The work of this article can provide a theoretical reference for the system parameter design of CHBR and the alternative control scheme under extreme load conditions.